The fuel cell is a static device which permits the direct conversion of chemical energy into electrical energy. As such, the fuel cell is not affected by the limitations of the Camot principle relating to thermal engines and is in fact characterised by high conversion efficiencies (50% or more with reference to the low heating value of the fed fuel). The most interesting types of fuel cells are those fed with air and hydrogen or a gas containing hydrogen, under pressure, usually from slightly above the atmospheric pressure to 3-5 bar. In particular, today attention is focused on the ion exchange polymeric membrane type, in view of its simplicity and for the potentially strong cost reduction. A type of design particularly suitable for membrane fuel cells is described in the U.S. Pat. No. 5,482,792. The technical development of the fuel cells today is extremely advanced, however their commercialisation is still far ahead due to the still high production costs, the lack of a reliable and efficient demonstrated design for the system of auxiliary components necessary to ensure the operation of the fuel cells, as well as of cost-effective availability of pure hydrogen or gas containing significant amount of hydrogen. This last problem is in fact overcome inside chemical complexes comprising electrochemical plants, typically chlor-alkali plants, chlorate electrolysis and hydrochloric acid electrolysis or refinery plants, which are characterised sometimes by the production of large amounts of by-product gases containing hydrogen. Electrochemical plants are particularly suitable for the integration with fuel cells, especially as the produced hydrogen is frequently very pure (chlor-alkali electrolysis, hydrochloric acid electrolysis) or can be easily purified (from traces of oxygen and chlorine, chlorate electrolysis). In addition, the electric energy produced by the fuel cells is typically of the direct type, same as the electric energy required by electrochemical plant electrolyzers. Therefore, in principle, it should be easy to integrate fuel cells into electrochemical plants, with the final result of substantially decreasing the overall consumption of electric power through the recovery of hydrogen. Conversely, in the case of chemical plants, the electric energy produced by the fuel cells should be converted into alternate current, which is the form of energy required by electric motors, heaters and other electrical apparatuses installed in these plants. The DC/AC converters of electric energy from direct to alternate current, known as inverters, are very expensive devices which make the assembly of the installation (fuel cellsxe2x80x94connection pipingxe2x80x94heat exchangersxe2x80x94inverterxe2x80x94electrical connection bus bars) economically disadvantageous with respect to the value of the produced electric energy.
These considerations take into account the interest shown since long towards the integration of fuel cells into electrochemical plants. An example of such an interest is the device described in the U.S. Pat. No. 4,778,579 which is representative of the state of the art. This device, as many others described in other patents, foresees the use of an adjuster of voltage which is directed to make compatible the two voltages at the two ends of the electrolyzer and of the fuel cells. These voltages vary as the current varies and, at a constant current, with the varying of time, as described in FIG. 2 of U.S. Pat. No. 4,778,579. The voltage adjusters suitable for electric power of electrochemical plants are expensive devices which have thus the same inconveniences of the aforementioned inverters, which make the installation of the system based on fuel cells hardly economically attractive.
It is the object of the present invention to provide a method for the direct integration of fuel cells in an electrochemical plant. By direct integration it is intended the connection of fuel cells to electrolyzers by means of bus bars without interposition of any voltage converter or adjuster or similar devices, used in the prior art.